Preparation And Electrochemical Study Of FeS/graphene Composites Based Anode Materials For Lithium-ion Battery

In recent years,as a transition metal sulfide,FeS has been considered as one of the promising anode materials for lithium ion batteries,due to its many advantages.Apart from the low cost and environmental benignity,it has a higher electrode potential than that of graphite,which can effectively limit the formation of SEI film.However,FeS as the anode for lithium ion batteries is still far from the commercialization due to some problems.For FeS,the product after discharge processes is an insulating polysulfide,which would limit the transport of the electrons and the diffusion of Li~+.In addition,FeS often suffers from large volume expansion during the charge-discharge processes,which can cause structure collapse and the deactivation of material.In this paper,we present three different methods to synthesize FeS/graphene composites and the corresponding pure FeS materials,which are homogeneous precipitation with ultrasonic treatment,hydrothermal reaction with high temperature heat treatment and direct precipitation with high temperature heat treatment.By comparing the feasibility of different synthesis methods in practical application and exploring the electrochemical performance of the composites to find a more reasonable method for the preparation of FeS/graphene composites.The main conclusions are summarized as follows:(1)FeS materials and FeS/G composites were prepared by homogeneous precipitation with direct ultrasound,and the morphology of the synthesized FeS is a tetragonal phase with irregular particles.And the FeS compounded with graphene has smaller particles and better dispersibility,but neither have high crystallinity.The test results indicate that the FeS/G composites exhibit higher electrochemical performance than that of the pure FeS electrode material,and the FeS/G composites demonstrated the high initial charge-discharge capacity of1477.3 mAh/g and 1115.2 mAh/g,respectively;at the current density of 100 mA/g,the discharge capacity of FeS/G is 567.2 mAh/g after 50 flakes and similar to wood chips.In the FeS/G composite material FeS microblocks are attached to both sides of graphene,forming a sandwich-like structure.In cycles,which is superior to that of the graphene(485.4 mAh/g)and FeS(286 mAh/g);the FeS/G composite material has better rate performance.On the other hand,the impedance of FeS/G is significantly lower than that of pure FeS materials.(2)The FeS/G composites and pure FeS material prepared by hydrothermal reaction with high temperature heat treatment have high crystallinity;the FeS material is in the form of flakes and similar to wood chips.In the FeS/G composites,the FeS particles are attached to both sides of graphene,and forming a sandwich-like structure.In addition,the charge transfer resistance of the two materials were lower,which are 63.38?and 27.66?,respectively.At the same time,the FeS/G electrode exhibited better cycling performance and rate performance,and compared to the pure FeS material,it was found that the composites prepared had higher Coulombic efficiency and better cycle stability.At the current density of 100 mA/g,the initial discharge capacity of FeS/G is 976.5 mAh/g,which is similar to graphene,and has poor cycle stability.(3)FeS/RGO composite materials and FeS materials were prepared by a simple method of direct precipitation with high temperature heat treatment.Some FeS particles in the FeS/RGO compositesl are tightly attached on both sides of the RGO layer,and part of it is wrapped in the RGO layer to form a structure which is similar to pea pods.This structural can relieve the large volume expansion during the charge-discharge processes.In addition,FeS/RGO composites are more porous and have a larger specific surface area than pure FeS materials.On the other hand,the electrochemical tests indicate that the FeS/RGO electrode exhibit higher electrochemical performance than that of FeS electrode electrode regardless of the cycle,the charge and discharge capacity of Fe S/RGO is higher than that of FeS.The results indicate that the FeS/RGO composites shows high Coulombic efficiency,excellent cycling and rate performances.